A comparison of gamma-irradiation-induced degradation in amphoterically Si-doped GaAs LED's and Zn-diffused GaAs LED's

A comparison is presented of the effects of gamma irradiation on the properties of amphoterically Si-doped GaAs LED's and Zn-diffused GaAs LED's. It is shown that the light output of GaAs:Si LED's is severely degraded by irradiation, and, in addition, that the light output cannot be recovered through forward-bias-induced annealing. In contrast, commercially available dome-shaped GaAs:Zn emitters with comparable power outputs degrade much less, and the degradation that is observed can be recovered by forward-bias-induced annealing. Further, this bias-induced recovery can be achieved by applying forward-current pulses only 10 to 50 ms in width. The lack of any bias-induced recovery in the GaAs:Si devices led to an investigation of gamma-induced deep levels using the transient capacitance method of deep level transient spectroscopy (DLTS). Following irradiation, two levels with thermal activation energies of 0.21 and 0.78 eV were observed. Subsequent forward bias reduced the concentration of the 0.21-eV level but had relatively little effect on the 0.78-eV level. These results suggest that the near midgap 0.78-eV level is one of the nonradiative recombination centers responsible for light output degradation.